Biological decontamination and surface sterilization is crucial throughout society: in military applications such as the decontamination of equipment and facilities exposed to deadly biological agents, or in a broad array of civilian applications including medical applications, food production and consumer goods. Chemical, heat, high-energy electron beams, x-ray or gamma-ray irradiation systems are presently used in commercial treatments; however, utilization of these systems may not be practical due to the cost, efficiency, immobility, electric power requirements, toxic waste, personal hazard and the time required to decontaminate items.
Over the last decade, considerable research has been conducted in using atmospheric plasmas as a decontamination method of surfaces. Atmospheric plasmas have the ability to generate unique radiolytic profiles. Research has shown that biological contaminants exposed to atmospheric plasmas can be sterilized in seconds to minutes. Atmospheric plasmas are fairly easy to produce; and, the equipment needed is relatively inexpensive. There are no hazardous wastes and the gaseous by-products can be locally controlled. Up to this time, utilization of atmospheric plasmas has been through sealed chambers and jets.
Atmospheric, non-equilibrium plasma (ANEP) is an example of a non-thermal processing method. There is a wide variance in the terminology for the process to produce such a plasma. In the literature, a variety of terminology is used to describe the phenomenon including atmospheric glow discharge, surface barrier discharge (SBD), dielectric barrier discharge (DBD), Single Dielectric Barrier Discharge (SDBD) and Surface Plasma Chemistry Process (SPCP). For convenience herein, the term dielectric barrier discharge (DBD) is used, without intending to exclude any of the ANEP plasma generating mechanisms implied by choosing a specific terminology for description of the technique herein.
FIG. 1 shows simplified examples of DBD configurations that may be used to produce an ANEP in an ambient air environment. A high voltage generator 10 applies an alternating current potential to a pair of metallic plates 20, 30, spaced apart from each other to form a region 50 in which an object may be placed. At least one dielectric layer 40 is disposed between a first plate 20 and the second plate 30. In this manner, the effect of the dielectric layer is to limit the current of any filamentary discharge that is formed between the plate 20, 30 so as to prevent the formation of a high current arc. The discharge in region 50 is thus limited in energy and results in an ANEP where variety of reactive species may be formed from the gas (He, O2, N2, CO2 and water vapor) and/or interaction with the packaged product. FIG. 1A shows a configuration with one dielectric layer 40 laid against an electrode 20. FIG. 1B shows an example where a dielectric plate 40 is laid against an electrode 20 and another dielectric plate 60 is laid against a second electrode 30. The charge accumulation on the plates which may be used in conjunction with the voltage waveform to estimate the power consumption may be measured by determining the voltage developed across a conventional capacitor 75. FIG. 1C illustrates a situation where a single dielectric layer 50 is disposed between the electrodes 20, 30, so that there are two regions 50 in which an ANEP may be produced.
As the possibility of an arc forming directly between the plates 20, 30 exists, by air paths around the dielectric, at least one electrode is often fully enclosed in an insulating material; and, the exposed electrode may be grounded. The insulating material may be the same material as used for the dielectric 40, 60; however, the two materials may have differing properties. For example, the dielectric plate may be quartz and the insulating material may be a moldable material.